1. Field of the Invention
The present invention relates to an exposure apparatus, and in particular to an exposure apparatus which is capable of improving illumination efficiency and performing uniform exposure.
2. Description of the Related Art
An exposure apparatus is known, which has an illumination optical system for illuminating a two-dimensional spatial light modulator (which hereinafter is referred to as a two-dimensional SLM) such as an LCD (liquid crystal display) or a DMD (digital micromirror device; trademark) with light from a light source, and which exposes an optical image controlled by the two-dimensional SLM onto a photosensitive material. The two-dimensional SLM must be uniformly illuminated in such an exposure apparatus. An optical integrator is used for the illumination optical system. The optical integrator is generally used for a projector as well as an exposure apparatus (e.g., see Japanese Patent Application Laid-Open (JP-A) No. 3-111806).
The optical integrator divides a luminous flux, passes the divided luminous fluxes through different paths and then re-couples the fluxes in order to eliminate a correlation between intensity and position (distribution of intensity) and to uniform the intensity. There provided two systems for the optical integrator in accordance with a system for dividing a luminous flux. (1) One is a fly-eye type for spatially dividing a luminous flux by using a lens array (fly-eye lens) in which lenses are two-dimensionally arranged. (2) The other is a rod type for angularly dividing a luminous flux by multiple reflection by using a glass rod or a hollow rod with its inner surface being a mirror.
In the fly-eye type, two fly-eye lenses are used. A first fly-eye lens converges light onto lens cells of a second fly-eye lens. A light source image is imaged on the lens cells of the second fly-eye lens. The second fly-eye lens images the images which are on lens cells of the first fly-eye lens onto a two-dimensional SLM. In the rod type, a light source image is imaged on an incident surface of a rod, and an image at the exit surface of the rod is imaged on a two-dimensional SLM.
When a lamp such as an ultrahigh pressure mercury-vapor lamp is used for a light source, the configuration of light-emitting portion of the lamp is totally different from the configuration of an illumination area of a two-dimensional SLM (i.e., the configuration of an area of the two-dimensional SLM to be illuminated). Nevertheless, the above-described integrator enables uniform illumination only on a required area on the two-dimensional SLM to be used.
In actuality, in the case that Etendue is large and the configuration of the light-emitting portion is different from the configuration of an area illuminated by the light reaching a two-dimensional SLM as in the case of a lamp, entire light emitted from the lamp cannot be effectively utilized, resulting in a decreased illumination efficiency.
A description will be given with a specific example. When a lamp and a fly-eye type integrator are used, an arc image of the lamp is imaged by a first fly-eye lens onto cells of a second fly-eye lens. When an area to be used on a two-dimensional SLM is formed in a rectangular, the lens cells of the fly-eye lens are formed in a similar configuration to the area to be illuminated in order to image images which are on the lens cell. It is designed so that the size of the arc image of the lamp is equal to or smaller than the size of the second fly-eye lens. Actually, however, it is difficult for all light source images to enter the lens cells because of the size of light source (the size of light-emitting portion of the lamp, i.e., the arc size), spread of light and aberration of lenses. For this reason, there arise problems in that an optical performance is deteriorated, illumination efficiency is decreased and uniformity of illumination is deteriorated.
In view of the above-described facts, an object of the present invention is to provide an exposure apparatus which is capable of obtaining high illumination efficiency and performing uniform exposure.